Polybenzimidazole is an non-melt processible polymer which exhibits high thermal stability as well as excellent resistance to solvent and oxidative degradation. This polymer possesses a very high melting temperature; when heated to high temperatures, it will usually decompose before melting. These characteristics have made polybenzimidazole desirable for use as a high temperature performance polymer.
Polybenzimidazole resin may be fabricated into a shaped article by the process described in U.S. Pat. No. 4,814,530 to Ward et al. Ward '530 describes a process of compacting a particulate, melt-derived polybenzimidazole resin in a mold under a pressure of 2,000 to 10,000 psi while heating the constrained resin to a temperature of 825.degree. to 950.degree. F. to form an article, and cooling the polybenzimidazole article while maintaining the pressure. Melt-derived polybenzimidazole particulates are produced by polymerizing an aromatic tetraamine and a diphenylester or an anhydride of an aromatic or heterocyclic dicarboxylic acid in a one or two stage process. This process of producing shaped articles has proven to be costly and inefficient for large scale production.
A more advantageous method of forming a polybenzimidazole-containing shaped article is by the process of cold compacting spray-atomization/quenched polybenzimidazole-containing particles. By this process, polybenzimidazole and other polymer resins may be processed alone or as blends by dissolving the resin(s) in a suitable solvent to form a dope, and atomizing the dope into a non-solvent atmosphere to form rounded particles which are cold compacted into a green body and sintered into a finished article. While spray-atomization/quenching produces particles exhibiting good density and compactability, particles size is often too large, and deficient in porosity for some applications.
Attempts have been made to reduce the size of melt-derived polybenzimidazole particles by ball and attrition milling, however, these methods have not produced particles exhibiting sufficiently high porosity and particles size reduction for some application. While spray-atomization/quenching particles exhibit a surface area, porosity and compactability greater than that of melt-derived particles, particle size is insufficiently low for many applications, i.e., plasma spraying deposition of thin polymer layers, mass transfer medium, injection molding into high density products, etc.